Blackmail is the crime of threatening to reveal embarrassing or damaging information about a person to the public, family or associates unless that person buys the blackmailer's silence.
Because the information is usually true, it is not revealing the information that is criminal, but demanding money – or other favours – in return for not releasing the information.
A blackmailer's "price" can also include sexual favours or that the person stay in a relationship. Both emotional and financial blackmail are forms of extortion.
Online blackmail can involve the posting of intimate photos on so-called 'revenge porn' websites (sites that maliciously, and without authorisation, publish intimate images) with demands for money to remove the photos.
There is also a disturbing related form of blackmail – where neither money nor favours are demanded – but a price is exacted all the same. Intimate images of women are stolen (often through illegal hacking) and then posted online. The photos may be posted along with home and work contact information, encouraging viewers to harass the woman. The price these blackmailers seek is humiliation of the other.
In a world where a female judge in Canada was suspended "because her husband put onto the web images taken in intimacy of her", rather than the authorities going after the man who violated her privacy, blackmail and related violence are serious threats for women and girls.
Revenge porn is in fact a gross violation of a woman's privacy, where private and personal video and photographic images are published without consent onto various websites for the purposes of extortion, blackmail and/or humiliation. This is an act of violence and should not be conflated with pornographic content.
Online blackmail is a mixed bag where blackmailers may steal intimate images or fake them. The price demanded may be money or physical and emotional control of the person being blackmailed. In the case of 'revenge porn' without financial motive, the price seems to be pure humiliation of women.